In manufacturing and employing integrated circuit devices, it is important that the devices operate properly. Completed integrated circuit devices are tested, and defective devices are discarded. The percentage of usable dies is called “silicon yield” because it indicates the fraction of usable integrated circuits in a manufactured lot. The large die size of some integrated circuit devices, such as programmable logic devices, results in fewer dies being produced per wafer. Because the number of usable dies significantly impacts profitability, it is important to enable the use of as many of the dies of the wafer as possible. More importantly, when a completed integrated circuit malfunctions after it has been installed in a finished product, such as a consumer electronics device, the malfunction of the integrated circuit may cause the entire product to fail.
Most integrated circuits are formed using a number of material layers. Each layer is patterned to add or remove selected portions to form circuit features that will eventually make up a complete integrated circuit. Various layers are formed above the die to enable connections to the elements of the die and the creation of certain devices, such as transistors. In manufacturing integrated circuits, plasma processing steps are often used to deposit or remove materials on semiconductor wafers, such as during etching or dielectric deposition. Plasma processing is well known in the art of manufacturing integrated circuits. However, the use of plasma may cause destructive charges (e.g., positive ions) to build up above the surface of the wafer. If the build up of the charge is large enough, and the charge has no leakage path to the wafer, a current will flow through the transistor gate oxide, causing damage to the gate oxide. In particular, the damage occurs when the ratio between the plasma collect area, commonly called the antenna area, and gate and diffusion areas exceeds a certain value. This damage is particularly severe for test structure devices, such as transistors having small gate and diffusion areas. Further, the minimum critical dimensions such as decreased gate areas of currently produced integrated circuits have also increased this ratio. The damage to the gate oxide may lead to performance degradation of the transistor, or result in reliability failures.
Another aspect of integrated circuit manufacturing where defects may occur is wire bonding. Wire bonds are used to connect a bond pad on one element of a device, such as a die, to a bond pad on another element, such as a substrate of the integrated circuit receiving the die. High voltage, such as electrostatic discharge (ESD) caused by handling and bonding, may damage the gate oxide.
Accordingly, there is a need for an improved method of and circuit for protecting a transistor formed on a die.